Automobile car door panels typically are formed of a thermoplastic substrate that can be formed using injection molding, thermoforming, extrusion or vacuum forming. It is often desired to cover sections of this panel with another material such as a synthetic fiber carpet or a fabric or another material. This covering can be for aesthetic and/or functional purposes.
Known production processes used for bonding materials to door panels require additional consumables. These can include, but are not limited to, glue, staples, clips and other mechanical means. Such additional consumables tend to affect the re-cyclability of the thermoplastic substrates to which the carpet/fabrics are bonded.
Other known bonding processes include linear or orbital vibration welding. U.S. Pat. Nos. 5,026,445 and 5,468,335, for example, disclose a thermoplastic substrate and a synthetic fiber carpet bonded together by a vibration welder generating frictional heat at an interface between the substrate and an underlying carpet. Specifically, both U.S. Pat. Nos. 5,026,445 and 5,468,335 disclose the use of a platen having a pattern of closely spaced pins. These pins are capable of penetrating the loft of a carpet and serve as energy directors with which a backing layer of the carpet can be welded to the thermoplastic substrate at the regions opposite to the pins.
The above-mentioned patents disclose welding processes that make use of the fact that thermoplastics will remelt with the application of heat and then resolidify once the heating ceases. These processes do not require mechanical devices for the attachment of the pieces to be welded.
One of the difficulties incurred in using the above-described welding processes is that they require the carpet layer to be subjected to localized contact either with ultrasonic horns or engaging pins used in vibration welding as taught by U.S. Pat. Nos. 5,026,445, 5,468,335. This localized contact, though indispensable for the disclosed processes, causes a marking or formation of telltale pin dents in the carpet welded to the plastic panel. To eliminate the dents it is then necessary to brush, comb or otherwise smooth out the effects of these processes upon the carpet surface.
Another difficulty in using the welding apparatus described in these patent is that the manufacture of platens with pins involves an expense.